According to sectarian including new cults Quranist & 19nrs , whom say they follow Quran alone but actually they follow their own fake messenger theory & appendixes which replacement of hadith. They think this term [seven repeated] is talking about Surah Fatiha [Chapter One from the Quran the opening].
Such understanding does create contradiction, such as "the Quran is separate from the chapter One [Sura Al-Fatiha]" Which does not make sense whatsoever. And The same word "Mathani/Repeated" has also been used on verse 39:23 and Allah clear say it is the most beautiful "Hadith/ Narration" which been repeated
However I have tried to understand this subject by looking into some verses from the Quran to find some clue what possible meaning could be for this [SEVEN REPEATED] but since Allah did not mention specifically therefore I take this issue also may be fall in the category of 3:7. Anyway here is some verses which I look into to find some clue.
VERSES RELATED TO TOPIC
The Quran 3:7
He it is Who has sent down to thee the Book: in it are verses basic or fundamental (of established meaning); they are the foundation of the Book: others are not of well-established meaning. But those in whose hearts is perversity follow the part thereof that is not of well-established meaning. Seeking discord, and searching for its interpretation, but no one knows its true meanings except Allah, and those who are firmly grounded in knowledge say: "We believe in it; the whole of it is from our Lord"; and none will grasp the Message except men of understanding
The Quran 39:23
Allah has revealed (from time to time) the most beautiful Message in the form of a Book, consistent with itself, (Yet) repeating (its teaching in various aspects): the skins of those who fear their Lord tremble thereat; then their skins and their hearts do soften to the celebration of Allah's praises. Such is the guidance of Allah: He guides therewith whom He pleases, but such as Allah leaves to stray, can have none to guide.
The Quran 2:209
If ye backslide after the clear (signs) have come to you, then know that Allah is Exalted in Power, Wise.
The Quran 2:251
By Allah's will, they routed them: and David slew Goliath; and Allah gave him power and wisdom and taught him whatever (else) He willed. And did not Allah check one set of people by means of another, the earth would indeed be full of mischief, but Allah is full of bounty to all the worlds.
The Quran 4:54
Or do they envy mankind for what Allah hath given them of His bounty? But We had already given the people of Abraham the Book and Wisdom and conferred upon them a great kingdom.
The Quran 34:6
And those to whom knowledge has come see that the (Revelation) sent down to thee from thy Lord― that is the Truth, and that it guides to the Path of the Exalted (in Might), Worthy of all praise
The Quran 45 :17
And We granted them clear Signs in affairs (of Religion): it was only after knowledge had been granted to them that they fell into schisms, through insolent envy among themselves. Verily thy Lord will judge between them on the Day of Judgement as to those matters in which they set up differences.
The Quran 20:99
Thus do We relate to thee some stories of what happened before: for We have sent thee a Message from Our own Presence.
We gave Moses the Book and followed him up with a succession of Messengers; We gave Jesus the son of Mary clear (Signs) and strengthened him with the holy spirit. Is it that whenever there comes to you a messenger with what ye yourselves desire not ye, are puffed up with pride? ―Some ye called impostors and others ye slay!
The Quran 4:153
The people of the Book ask thee to cause a book to descend to them from heaven: indeed they asked Moses for an even greater (miracle), for they said: "Show us Allah in public" but they were dazed for their presumption, by thunder and lightning. Yet they worshipped the calf even after clear signs had come to them; even so We forgave them; and gave Moses manifest proofs of authority
The Quran 21:74
And to Lut, too, we gave Judgment and Knowledge, and We saved him from the town which practised abominations: truly they were a people given to Evil, a rebellious people
The Quran 21:48
In the past We granted to Moses and Aaron the Criterion (for judgment) and a Light and a Message for those who would do right― (48) Those who fear their Lord in their most secret thoughts, and who hold the Hour (of Judgment) in awe.
The Quran 21:79
To Solomon We inspired the (right) understanding of the matter: to each (of them) We gave Judgment and Knowledge; it was Our power that made the hills and the birds celebrate Our praises with David: it was We Who did (these things).
The Quran 27:15
We gave (in the past) knowledge to David and Solomon: and they both said: "Praise be to Allah, Who has favoured us above many of His servants who believe!"
The Quran 31:12
We bestowed (in the past) wisdom on Luqman: "Show (thy) gratitude to Allah." Any who is (so) grateful does so to the profit of his own soul: but if any is ungrateful verily Allah is free of all wants, worthy of all praise.
The Quran 40:53
We did aforetime give Moses the (Book of) Guidance, and We gave the Book in inheritance to the Children of Israel―
To his son came the command): "O Yahya! Take hold of the Book with might": and We gave him wisdom even as a youth.
The Quran 3:79
It is not for any human being to whom Allah has given the Book and Al-Hukm and Prophethood to say to the people: "Be my worshippers rather than Allah's." On the contrary "Be you Rabbaniyyun , because you are teaching the Book, and you are studying it.
The Quran 16:2
He sends down the angels with the ruh (revelation) of His Command to whom of His slaves He wills: "Warn mankind that La ilaha illa Ana (none has the right to be worshipped but I), so fear Me
The Quran 2:87
And indeed, We gave Musa (Moses) the Book and followed him up with a succession of Messengers. And We gave 'Îsa (Jesus), the son of Maryam. clear signs and supported him with ruh-ul-Qudus . Is it that whenever there came to you a Messenger with what you yourselves desired not, you grew arrogant? Some you disbelieved and some you killed.
MAIN POINTS FROM ABOVE VERSES
[3:7] true believer will believe every verses regardless they understand it or NOT
[39:23] Some beautiful Hadith/event in the Quran do repeat to make the issue more clear
[2:209] AL- BAYINAT [clear prove] & some other verse prove other messenger/prophets also received Al-Bayinat too.
[2:251] Allah given KINGDOM to Dawood [P] [& other prophets also].
[4:54] Prophet Abraham was also given the BOOK, WISDOM & KINGDOM
[34:6] The mankind gain knowledge through their Messenger/Prophet should able to recognise the Ayat of Allah.
[45:17] This indicate it was given to THEM [which mean all prophet] AL-BAYINAT[clear Signs]
[2:87] This indicate Isa[P] also received AL-BAYINAT [clear signs]
[4:153] Prophet Mosa[P] has also the AL-BAYINAT & SULTAN [authority]
[21:74] Prophet Lut[P] has also given the JUDGEMENT & KNOWLEDGE.
[21:48] Prophet Moses and Aaron was also granted The CRITERION
[21:79] Prophet Solomon was given UNDERSTANDING / JUDGEMENT & KNOWLEDGE.
[27:15] The KNOWLEDGE was given to David[P] & Solomon[P]
[31:12] Lukman [P] was also given WISDOM
[40:53] Prophet Moses [P] was also given the GUIDANCE.
[19:12] Some prophet got WISDOM from youth.
[3:79] indicate Allah given Prophethood .
[16:2] Allah send angel & [ruh/ (revelation]
[2:87] This indicate Prophet was Isa [p] gaven/ supported him with ruh-ul-Qudus.
THE MAIN VERSE OF THE TOPIC [15:87]
Certainly We have given you saba almathani [the seven oft-repeated] and the great Quran.
It is very important to understand that the above verse dose NOT contain the term AYAT [Verse/Sign].So how can them sectarian ,say it is talking about seven verse of chapter one ?
However the only reason they say as such is because of the so-called hadith, which has so many fake story regarding this. and because of so many narration the sectarian is confused on the issue of Sura Fahtiha, some say it is FARD/obligatory to read in SALAH & some say it is only Suunah or Wazeeb.
However it's very important that we must NOT say anything as a fact on such issue, since Allah did not mention specifically or clearly [about this seven repeated ].
Anyway in that respect, I have given only nine example [out of several other example which can be found in the Quran] I think the highest possibility of any seven things, [from the list below] which has been repeated and given to Messenger /Prophet Mohammed [P] as well as others Prophets.
[THE CLEAR PROOF]
Finally, since this is not an issue, therefore I should not be bother too much regarding this, since it is a matter between Allah and HIS Messenger / Prophet only ALLAH KNOWS BEST what he given to His messenger / prophets .